1. Field of the Invention
The invention relates to a process for biologically treating organic materials. In particular, this invention provides a process for treating sewage sludge resulting from the treatment of municipal waste waters and the like to remove volatile solids and other contaminants and generate biogas.
2. Description of the Related Art
Since the passage of the Clean Water Act many industries have been required to institute treatment programs for the waste water they generate before these waters are discharged into public drains and waterways. These programs often include on-site waste water treatment processes, discharge into public treatment works or both.
Waste water is the term used for water which has been changed after household, commercial and industrial use, in particular water which is contaminated and flows and passes into the drainage channels.
Waste water typically contains a wide variety of contaminants which must be removed prior to discharge into public waterways and such contaminants include: organic matter, such as proteins, carbohydrates and lipids; chemicals, such as pesticides, insecticides, heavy metals and fertilizers; and sewage. The waste water is typically assessed in terms of its biochemical oxygen demand (BOD), total suspended solids (TSS) and dissolved oxygen (DO). Another important class of constituents that must be removed from waste water is the volatile organic compounds (VOC) which cause or contribute to the odor of waste water.
A number of processes have been developed which are directed at specific contaminants found in waste water, for example: phenol oxidases and hydrogen peroxide have been used to decolorize pulp and paper mill waste water (U.S. Pat. No. 5,407,577); enzymes from an atypical strain of Bacillus stearothermophilus have been used to degrade algal cell walls (U.S. Pat. No. 5,139,945); a combination of bacteria and enzymes have been used to improve the water quality of standing bodies of water (U.S. Pat. No. 5,227,067); cellulases have been used to digest wood/paper compositions (U.S. Pat. No. 5,326,477); Xanthomonas maltophilia and Bacillus thuringiensis have been used to degrade polar organic solvents (U.S. Pat. No. 5,369,031); yeast has been used to digest carbohydrate-containing waste water (U.S. Pat. No. 5,075,008); a combination of beta.-glucanase, alpha.-amylase and proteases have been used to digest microbial slime (U.S. Pat. No. 5,071,765); and a combination of amylase, lipase and/or proteases have been used to digest colloidal material such as starch, grease, fat and protein (U.S. Pat. No. 5,882,059). However, each of these compositions are directed at only a specific contaminant and they do not address the variety of contaminants which are usually found in waste water and other polluted water. A composition described in U.S. Pat. No. 3,635,797 used a yeast fermentation composition to deodorize sewage ponds and degrade organic waste. However, this composition has been found to be unstable and yielded variable results from one batch to another.
The above processes are generally carried out under aerobic conditions, that is, the treating process requires the presence of oxygen, usually from air.
The present inventors have invented a liquid composition comprising fermentation supernatant from a yeast such as a Saccharomyces cerevisiae culture and a non-ionic surfactant, preferably selected from the group consisting of ethoxylated alkylphenols and/or long chain aliphatic alcohols. This liquid composition in combination with the active enzymes, resulting from the fermentation of Saccharomyces cerevisiae, has been used under aerobic conditions, as well as anaerobic conditions to treat, among other waste waters, municipal sewage. (See U.S. Pat. Nos. 5,820,758; 5,849,566; 5,879,928; 5,885,590 and published U.S. patent application Ser. No. 12/586,126.) It has now been surprisingly found that a product comprising the combination of a fermentation supernatant from a Saccharomyces cerevisiae culture, which is free of active enzymes and a non-ionic surfactant is effective to treat sewage sludge, e.g. a sewage sludge resulting from the treatment of municipal or industrial waste water. This discovery is discussed in more detail below.
The biological treatment of liquids contaminated with organic materials or the purification of waste water to remove organic contaminants, which contaminants are contained in the liquids in a dissolved, colloidal or finely dispersed form, by microbial activity, e.g. by anaerobic degradation, generates a combustible gas, known as biogas.
Generally, waste water is biologically purified in waste treatment plants using the same or similar procedures which occur when the waste water biologically cleans itself in running waters, i.e. under aerobic conditions, albeit, in a technically more intensive manner. In nature, the anaerobic process of biological purification likewise occurs, e.g. at the bottom of flat, still waters.
For the purposes of describing the present invention, it is understood that “treating” means the conversion of organic materials, i.e. contaminants, by means of micro-organisms, e.g. bacteria, in the presence or absence of oxygen. During the process of anaerobic degradation of organic materials, biogas is produced, i.e. a gas mixture which consists of methane, mainly, and carbon dioxide and traces of other ingredients. The process of the invention may also be carried out under aerobic conditions to provide fermentation products from cellulosic feeds, etc.
Methods for biologically treating liquids, containing high amounts of organic materials as contaminants, under anaerobic conditions are known for treating waste waters from the foodstuff industry, agriculture, mineral oil industry as well as from pulp making. In other words, it is possible to treat many liquids but, in general, such known biological methods are incapable of providing a full purification or complete conversion of such organic contaminants.
It is one object of this invention to treat an organic waste material, in a bacterial process, by digesting said waste at an elevated temperature to produce biogas, which biogas can be used in generators for electricity production and/or in boilers for heating purposes.
It is another object of the invention to treat sewage sludge in a bacterial process by fermenting said sludge at an elevated temperature to produce a biogas, which can then be used in generators for electricity production and/or in boilers for heating purposes and, in particular said biogas may be used to provide the heat to treat said sewage sludge.
It is another object of the invention to treat sewage sludge in a bacterial process that is carried out by fermenting said sludge at an elevated temperature to reduce the volatile organic solids (VOS).
It is another object of the invention to treat sewage sludge in a bacterial process that is carried out by fermenting said sludge at an elevated temperature to reduce the weight and/or volume of the treated, solid sludge product leaving the process.
Other objects of this invention will become apparent from a reading of the present specification.